Methods and devices for determining an availability of a synchronization source

ABSTRACT

The present disclosure relates to a method for determining an availability of a synchronization source in a communication system. The method comprises: detecting a stability of the synchronization source when the synchronization source recovers from a failure; and determining the availability of a synchronization source based on the detected stability of the synchronization source. The present disclosure also relates to network devices and a computer readable medium for performing said method.

CROSS REFERENCE TO RELATED APPLICATION

This application is a 35 U.S.C. § 371 national stage application of PCTInternational Application No. PCT/CN2017/113071, filed on Nov. 27, 2017,the disclosure and content of which is incorporated herein by referencein its entirety.

TECHNICAL FIELD

This disclosure generally relates to a communication system, and inparticular to methods and device for determining an availability of asynchronization source in a communication system.

BACKGROUND

Various components or devices operating in a communication systemtypically require a synchronization between them due to a demand ofcooperation. Thus, the communication system typically provides thosecomponents or devices with several synchronization source candidates sothat those components or devices may select one of synchronizationsource candidates as a reference.

A synchronization source might fail due to many factors. If selectedsynchronization source fails, another one of synchronization sourcecandidates may be selected as the reference. In this case, even if thefailing synchronization source recovers from the failure condition, itmay not be considered an available candidate for those components ordevices that select synchronization source candidate because thesynchronization source might experience a failure again.

SUMMARY

The summary is provided to introduce a selection of concepts in asimplified form that are further described below in detaileddescription. This summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter.

To avoid a ping-pong switching of a synchronization source due to arepeated failure, the wait-to-restore time (WTR) is introduced. The WTRapplies when a failing synchronization source recovers from a failurecondition to observe whether the synchronization source fails againwithin the WTR. If the synchronization source does not fail again whenthe WTR expires, the synchronization source may be considered anavailable candidate again. Thus, the introduction of the WTR may ensurethat a previous failed synchronization source is fault-free for acertain time (i.e., the WTR).

However, the WTR is fixed and cannot be adjusted, especially cannot beadjusted automatically once it is configured. Thus, the manner of theWTR lacks flexibility and might waste time if the WTR is too long.Besides, the WTR cannot handle an instable state for a synchronizationsource that is referred to as flap. The flap means that asynchronization source changes from a traceable state to a failingstate, and then a traceable state again during a period. The WTR alsocannot differentiate between a synchronization source in which flapoccurs frequently and a synchronization source in which flap occurs lessfrequently. Hence, there is a need for a solution addressing the aboveissues.

In general, embodiments of the present disclosure provide a solution forsolving the issues of synchronization source as discussed above.

According to a first aspect of the present disclosure, a method fordetermining an availability of a synchronization source in acommunication system is provided. The method may comprise detecting astability of the synchronization source when the synchronization sourcerecovers from a failure; and determining the availability of asynchronization source based on the detected stability of thesynchronization source.

According to one or more embodiments of the first aspect of the presentdisclosure, the detecting the stability of the synchronization sourcewhen the synchronization source recovers from the failure may comprise:starting a first period when the synchronization source recovers fromthe failure; detecting within the first period whether there is the flapoccurred in the synchronization source; identifying the synchronizationsource as instable if the flap is detected in the synchronizationsource; or identifying the synchronization source as stable if no flapis detected in the synchronization source.

According to one or more embodiments of the first aspect of the presentdisclosure, identifying the synchronization source as instable furthermay comprise: setting a penalty value and a count for the flap detectedin the synchronization source; increasing the penalty value and thecount; starting a second period; detecting within the second periodwhether there is another failure in the synchronization source;restarting the first period when the synchronization source recoversfrom the another failure if the another failure is detected in thesynchronization source; or decreasing the penalty value if no anotherfailure is detected in the synchronization source; comparing decreasedpenalty value with a threshold; if the decreased penalty value is largerthan or equal to the threshold: identifying the synchronization sourceas instable; restarting the second period; or if the decreased penaltyvalue is less than the threshold: identifying the synchronization sourceas stable.

According to one or more embodiments of the first aspect of the presentdisclosure, determining the availability of the synchronization sourcebased on the detected stability of the synchronization source mayfurther comprise: determining the synchronization source as available ifthe synchronization source is identified as stable; or determining thesynchronization source as unavailable if the synchronization source isidentified as instable.

According to one or more embodiments of the first aspect of the presentdisclosure, determining the availability of a synchronization sourcebased on the detected stability of the synchronization source mayfurther comprise: determining the synchronization source as availableeven if the synchronization source is identified as instable in the casethat the synchronization source is used originally and/or the penaltyvalue of the synchronization source is the smallest among allsynchronization sources if all synchronization sources are identified asinstable.

According to one or more embodiments of the first aspect of the presentdisclosure, the method may further comprise generating an alarm when thesynchronization source is determined as available.

According to one or more embodiments of the first aspect of the presentdisclosure, the penalty value, the count, the threshold, the firstperiod, and the second period may be configurable.

According to one or more embodiments of the first aspect of the presentdisclosure, initial values of the penalty value and the count may beconfigured to be zero.

According to one or more embodiments of the first aspect of the presentdisclosure, the method may further comprise configuring a maximum valueof the penalty value such that the penalty value does not continue toincrease when the penalty value reaches the maximum value.

According to one or more embodiments of the first aspect of the presentdisclosure, the penalty value may be based on the count.

According to one or more embodiments of the first aspect of the presentdisclosure, decreasing the penalty value may comprise decreasing penaltyvalue faster than increasing the penalty value.

According to one or more embodiments of the first aspect of the presentdisclosure, decreasing penalty value faster than increasing the penaltyvalue may comprise decreasing the penalty value exponentially.

According to a second aspect of the present disclosure, a network devicefor determining an availability of a synchronization source in acommunication system is provided. The network device may comprise: aprocessor; and a memory communicatively coupled to the processor andadapted to store instructions which, when executed by the processor,cause the network device to perform operations of: detecting a stabilityof the synchronization source when the synchronization source recoversfrom a failure; and determining the availability of a synchronizationsource based on the detected stability of the synchronization source.

According to one or more embodiments of the second aspect of the presentdisclosure, the operation of detecting the stability of thesynchronization source when the synchronization source recovers from afailure may comprise operations of: starting a first period when thesynchronization source recovers from the failure; detecting within thefirst period whether there is the flap occurred in the synchronizationsource; identifying the synchronization source as instable if the flapis detected in the synchronization source; or identifying thesynchronization source as stable if no flap is detected in thesynchronization source.

According to one or more embodiments of the second aspect of the presentdisclosure, the operation of identifying the synchronization source asinstable may further comprise operations of: setting a penalty value anda count for the flap detected in the synchronization source; increasingthe penalty value and the count; starting a second period; detectingwithin the second period whether there is another failure in thesynchronization source; restarting the first period when thesynchronization source recovers from the another failure if the anotherfailure is detected in the synchronization source; or decreasing thepenalty value if no another failure is detected in the synchronizationsource; comparing decreased penalty value with a threshold; if thedecreased penalty value is larger than or equal to the threshold:identifying the synchronization source as instable; restarting thesecond period; or if the decreased penalty value is less than thethreshold: identifying the synchronization source as stable.

According to one or more embodiments of the second aspect of the presentdisclosure, the operation of determining the availability of thesynchronization source based on the detected stability of thesynchronization source may further comprise operations of: determiningthe synchronization source as available if the synchronization source isidentified as stable; or determining the synchronization source asunavailable if the synchronization source is identified as instable.

According to one or more embodiments of the second aspect of the presentdisclosure, the operation of determining the availability of asynchronization source based on the detected stability of thesynchronization source may further comprise operations of: determiningthe synchronization source as available even if the synchronizationsource is identified as instable in the case that the synchronizationsource is used originally and/or the penalty value of thesynchronization source is the smallest among all synchronization sourcesif all synchronization sources are identified as instable.

According to one or more embodiments of the second aspect of the presentdisclosure, the network device may further comprise an operation ofgenerating an alarm when the synchronization source is determined asavailable.

According to one or more embodiments of the second aspect of the presentdisclosure, wherein the penalty value, the count, the threshold, thefirst period, and the second period may be configurable.

According to one or more embodiments of the second aspect of the presentdisclosure, wherein initial values of the penalty value and the countmay be configured to be zero.

According to one or more embodiments of the second aspect of the presentdisclosure, the network device may further comprise an operation ofconfiguring a maximum value of the penalty value such that the penaltyvalue does not continue to increase when the penalty value reaches themaximum value.

According to one or more embodiments of the second aspect of the presentdisclosure, wherein the penalty value may be based on the count.

According to one or more embodiments of the second aspect of the presentdisclosure, wherein the operation of decreasing the penalty value maycomprise an operation of decreasing penalty value faster than increasingthe penalty value.

According to one or more embodiments of the second aspect of the presentdisclosure, wherein the operation of decreasing penalty value fasterthan increasing the penalty value may comprise an operation ofdecreasing the penalty value exponentially.

According to the third aspect of the present disclosure, anon-transitory computer readable medium is provided. The non-transitorycomputer readable medium has a computer program stored thereon which,when executed by a processor, causes the processor to perform the methodaccording to the first aspect of the present disclosure.

According to embodiments of the present disclosure, the availability ofthe synchronization source can be determined in a flexible manner andthe stability of synchronization source for the components or devicescan be enhanced.

BRIEF DESCRIPTION OF THE DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and benefits of variousembodiments of the present disclosure will become more fully apparent,by way of example, from the following detailed description withreference to the accompanying drawings, in which like reference numeralsor letters are used to designate like or equivalent element. Thedrawings are illustrated for facilitating better understanding of theembodiments of the disclosure and not necessarily drawn to scale, inwhich:

FIG. 1 is a schematic diagram illustrating different types ofsynchronization sources.

FIG. 2 is a block diagram illustrating different states ofsynchronization sources.

FIG. 3 is a flowchart schematically illustrating a method fordetermining an availability of a synchronization source in acommunication system according to an embodiment of the presentdisclosure.

FIG. 4 is a block diagram of a network device for determining anavailability of a synchronization source in a communication systemaccording to an embodiment of the present disclosure.

FIG. 5 is a block diagram of another network device for determining anavailability of a synchronization source in a communication systemaccording to an embodiment of the present disclosure.

FIG. 6 is a flowchart schematically illustrating a process fordetermining an availability of a synchronization source in acommunication system according to an embodiment of the presentdisclosure.

DETAILED DESCRIPTION

Hereinafter, the principle and spirit of the present disclosure will bedescribed with reference to illustrative embodiments. It should beunderstood, all these embodiments are given merely for one skilled inthe art to better understand and further practice the presentdisclosure, but not for limiting the scope of the present disclosure.For example, features illustrated or described as part of one embodimentmay be used with another embodiment to yield still a further embodiment.In the interest of clarity, not all features of an actual implementationare described in this specification.

References in the specification to “one embodiment”, “an embodiment”,“an example embodiment”, etc. indicate that the embodiment described mayinclude a particular feature, structure, or characteristic, but it isnot necessary that every embodiment includes the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

It shall be understood that although the terms “first” and “second” etc.may be used herein to describe various elements, these elements shouldnot be limited by these terms. These terms are only used to distinguishone element from another. For example, a “first” element could also bereferred to as a “second” element, and similarly, a “second” elementcould also be referred to as a “first” element, without departing fromthe scope of example embodiments. As used herein, the term “and/or”includes any and all combinations of one or more of the associatedlisted items.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be liming of exampleembodiments. As used herein, the singular forms “a”, “an”, and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises”, “comprising”, “has”, “having”, “includes”, and/or“including”, when used herein, specify the presence of stated features,elements, and/or components etc., but do not preclude the presence oraddition of one or more other features, elements, components and/orcombinations thereof.

As used herein, the term “communication system” refers to a networkfollowing any suitable communication standards, such as LTE-Advanced(LTE-A), LTE, Wideband Code Division Multiple Access (WCDMA), High-SpeedPacket Access (HSPA), and so on. Furthermore, the communications betweena terminal device and a network device in the wireless communicationnetwork may be performed according to any suitable generationcommunication protocols, including, but not limited to, the firstgeneration (1G), the second generation (2G), 2.5G, 2.75G, the thirdgeneration (3G), the fourth generation (4G), 4.5G, the future fifthgeneration (5G) communication protocols, and/or any other protocolseither currently known or to be developed in the future.

The term “network device” refers to a device in a wireless communicationnetwork via which a terminal device accesses the network and receivesservices therefrom. The network device refers a base station (BS), anaccess point (AP), a Mobile Management Entity (MME),Multi-cell/Multicast Coordination Entity (MCE), a gateway, a server, acontroller or any other suitable device in the wireless communicationnetwork. The BS may be, for example, a node B (NodeB or NB), an evolvedNodeB (eNodeB or eNB), a gNB, a Remote Radio Unit (RRU), a radio header(RH), a remote radio head (RRH), a relay, a low power node such as afemto, a pico, and so forth.

Yet further examples of network device include multi-standard radio(MSR) radio equipment such as MSR BSs, network controllers such as radionetwork controllers (RNCs) or base station controllers (BSCs), basetransceiver stations (BTSs), transmission points, transmission nodes,Multi-cell/multicast Coordination Entities (MCEs), core network nodes(e.g., MSCs, MMEs), O&M nodes, OSS nodes, SON nodes, positioning nodes(e.g., E-SMLCs), and/or MDTs. More generally, however, network devicemay represent any suitable device (or group of devices) capable,configured, arranged, and/or operable to enable and/or provide aterminal device access to the wireless communication network or toprovide some service to a terminal device that has accessed the wirelesscommunication network.

Wherein, the term “terminal device” refers to any end device that canaccess a wireless communication network and receive services therefrom.By way of example and not limitation, the terminal device refers to amobile terminal, UE, or other suitable device. The UE may be, forexample, a Subscriber Station (SS), a Portable Subscriber Station, aMobile Station (MS), or an Access Terminal (AT). The terminal device mayinclude, but not limited to, portable computers, image capture terminaldevices such as digital cameras, gaming terminal devices, music storageand playback appliances, a mobile phone, a cellular phone, a smartphone, a tablet, a wearable device, a personal digital assistant (PDA),a vehicle, and the like. The terminal device may supportdevice-to-device (D2D) communication, for example by implementing a 3GPPstandard for sidelink communication, and may in this case be referred toas a D2D communication device.

In the following description and claims, unless defined otherwise, alltechnical and scientific terms used herein have the same meaning ascommonly understood by one of ordinary skills in the art to which thisdisclosure belongs.

Devices or components in a communication system may be provided with aplurality of different types of synchronization sources. For example,devices or components may be provided with a synchronization source froma Radio Base Station (RBS), a synchronization source from a GlobalPosition System (GPS), a synchronization source from a Precision TimeProtocol (PTP) network 1, and a synchronization source from aSynchronous Optical Network (SONET) 2, as shown in FIG. 1. In the caseof FIG. 1, the time reference of the PTP network 1 may be from a masterclock and the time reference of master clock may be from GPS. That is,the PTP network 1 may either receive a synchronization source or providea synchronization source. It can be seen in FIG. 1 that there may be alot of different types of synchronization sources for devices orcomponents in a communication system. It will be appreciated that thesynchronization sources for devices or components in a communicationsystem are not limited to those shown in FIG. 1.

When devices or components in a communication system are provided with aplurality of different types of synchronization sources, they may selectone of those synchronization sources as a reference. As shown in FIG. 2,a device may select the synchronization source 1 as reference among foursynchronization sources 1-4. The synchronization source 2 and thesynchronization source 3 may be available candidates. However, thesynchronization source 4 may be unavailable due to some factors, e.g.failing. That is, those synchronization sources may have differentstates. If the synchronization source 4 fails repeatedly after arecovery and being a candidate, a ping-pong switching of thesynchronization source 4 is possible.

To avoid a ping-pong switching of a synchronization source due to arepeated failure, the wait-to-restore time (WTR) is introduced. The WTRapplies when a failing synchronization source recovers from a failurecondition to observe whether the synchronization source fails againwithin the WTR. If the synchronization source does not fail again whenthe WTR expires, the synchronization source may be considered anavailable candidate again. Thus, the introduction of the WTR may ensurethat a previous failed synchronization source is fault-free for acertain time (i.e., the WTR).

However, the WTR is fixed and cannot be adjusted, especially cannot beadjusted automatically once it is configured. Thus, the manner of theWTR lacks flexibility and might waste time if the WTR is too long.Besides, the WTR cannot handle an instable state for a synchronizationsource that is referred to as flap. Herein flap means that asynchronization source changes from a traceable state to a failingstate, and then a traceable state again during a period. The WTR alsocannot differentiate a synchronization source in which flap occursfrequently and a synchronization source in which flap occurs lessfrequently.

There is hence a need for a solution addressing the issues as discussedabove.

FIG. 3 is a flowchart schematically illustrating a method fordetermining an availability of a synchronization source in acommunication system according to an embodiment of the presentdisclosure. With reference to FIG. 3, in accordance with an embodimentof the present disclosure, a method 300 for determining an availabilityof a synchronization source in a communication system may comprisedetecting a stability of a synchronization source when thesynchronization source recovers from a failure at block 310. As statedabove, even if a failing synchronization source recovers from a failurecondition, it may not be considered an available candidate because thesynchronization source might not be stable due to flap. Thus, method 300may first detect a stability of the synchronization source that recoversfrom a failure to avoid a ping-pong switching of the synchronizationsource even though a flap occurs in the synchronization source.

After detecting the stability of the synchronization source, method 300may determine the availability of a synchronization source based on thedetected stability of the synchronization source at block 320. That is,according to method 300, the availability of a synchronization source isbased on the detected stability of the synchronization source and thusthe availability of a synchronization source may vary dynamically overthe change of stability of the synchronization source. Thus, method 300may determine dynamically the availability of a synchronization sourcein a flexible manner instead of determining the availability of asynchronization source based on only the status of the synchronizationsource in a fixed WTR, as described below.

In an exemplary embodiment according to method 300, detecting thestability of the synchronization source when the synchronization sourcerecovers from a failure may comprise starting a period, which could becalled a first period, when the synchronization source recovers from thefailure to detect within the first period whether there is flap occurredin the synchronization source. Since a flap might occur in thesynchronization source once the synchronization source recovers from thefailure, it is necessary that detecting whether a flap occurs in thesynchronization source in an observation period after thesynchronization source recovers from the failure. Thus, the first periodshould start at a recovery of the synchronization source.

In contrast to the WTR that is fixed once it is configured, the firstperiod according to method 300 may be configurable or adjustable. Theconfigurable or adjustable first period may cause a process of detectinga flap to be shortened, lengthened, or terminated automatically ormanually at any time based on a state of the synchronization sourceand/or a demand. For example, the first period may be shortened in acase that a flap occurs scarcely in the synchronization source accordingto a history record. That is, when a synchronization source may beconsidered always stable and trusted according to a history record, theprocess of detecting a flap, i.e., detecting the stability of thesynchronization source, thus can be shortened to save time and improveefficiency. In contrast, the first period may be lengthened in a casethat flap occurs frequently in the synchronization source according tohistory record. That is, when a the synchronization source may beconsidered always instable and untrusted according to a history record,the process of detecting a flap, i.e., detecting the stability of thesynchronization source, thus can be lengthened to ensure that thesynchronization source may be a candidate again only if it is reallystable. In some embodiments, the first period may be terminated by ahuman operator in a case that the human operator considers thesynchronization source stable. Obviously, a configurable or adjustablefirst period may deal with various situations of a synchronizationsource in a more flexible manner.

According to method 300, after a detection of a synchronization source,a stability of the synchronization source may be identified based on theresult of the detection. The result may include that a flap is detectedin the synchronization source within the first period or no flap isdetected in the synchronization source within the first period. In thiscase, a synchronization source may be identified as instable if a flapis detected in the synchronization source within the first period. Incontrast, a synchronization source may be identified as stable if noflap is detected in the synchronization source within the first period.

In an exemplary embodiment, if a synchronization source is identified asinstable, it may still be detected continually. However, if thesynchronization source is still instable after one or more detectingperiods, e.g., after one or more first periods, the stability of thesynchronization source might be considered worse. Moreover, the longertime is taken by a synchronization source to reach a stable state, theworse the stability of the synchronization source is. Since a frequencyand/or number of occurrence of flap may be used to differentiatedifferent stabilities and thus determine an availability, detecting themis important and meaningful for determining an availability of asynchronization source based on a stability of a synchronization source.Therefore, identifying the synchronization source as instable mayfurther comprise setting a penalty value and a count for a flap detectedin the synchronization source. In this case, the penalty value may beconsidered a figure-of the merit of stability, which helps to indicate adegree of a stability of a synchronization source. In this way, a bettersource can be selected from many sources by means of the penalty valueeven if those sources are all identified as instable.

In view of the above, therefore, method 300 may comprise increasing thepenalty value and the count once a flap is detected, which means that astability of synchronization source is getting worse. The larger penaltyvalue and count may means that a stability of a synchronization sourceis worse. The penalty value and the count may be configurable oradjustable to indicate a degree of a stability of a synchronizationsource as demand. In some embodiments, initial values of the penaltyvalue and the count may be configured to be zero. In some embodiments,method 300 may further comprise configuring a maximum value of thepenalty value such that the penalty value does not continue to increasewhen the penalty value reaches the maximum value. The reasons why amaximum value of the penalty value is configured in that if asynchronization source is very instable during detection and thus thepenalty value might be increased to an extreme large value so that thesynchronization source can become no longer a candidate, it isundesired. Thus, configuring the maximum value of the penalty value canavoid a loss of a synchronization source. In some embodiments, thepenalty value may be based on the count. That is, the penalty value maybe associated with the count and the penalty value may be calculatedbased on count to become a function of the count.

Although increasing the penalty value and count means a worse stabilityof a synchronization source, the stability of the synchronization sourcewith the penalty value and count might change over time, e.g., a flapoccurs more frequently, infrequently or hardly over time. Therefore, achance is required to be provided to further indicate a stability of thesynchronization source. In this case, method 300 may comprise starting asecond period to further detect within the second period whether thereis another failure in the synchronization source. Similar to the firstperiod, the second period also may be configurable or adjustable.

If another failure is detected in a synchronization source within thesecond period, method 300 may restart the first period when thesynchronization source recovers from the another failure. That is, inthe case that the synchronization source recovers from a failure againand thus might become a candidate, the stability of the synchronizationsource is required to be detected continually. The acts that need to beperformed within the first period are already described above and thusthey are not described again in detail herein.

If no another failure is detected in the synchronization source withinthe second period, which at least means that the synchronization sourcemight be stable within the second period, then the penalty value will bedecreased to indicate that the stability of the synchronization sourceis getting better. In some embodiments, if a synchronization sourcemight be required to be a candidate as fast as possible, then decreasingthe penalty value may comprise decreasing penalty value faster thanincreasing the penalty value. In an exemplary embodiment, decreasingpenalty value faster than increasing the penalty value may comprisedecreasing the penalty value exponentially. It will be appreciated bythose skilled in the art that decreasing the penalty value as fast aspossible or faster than increasing the penalty value can be achieved byany suitable manner and thus is not limited to only decreasing thepenalty value exponentially.

It can be determined based on the above that the smaller penalty valuemeans better stability of a synchronization source. When the penaltyvalue is small enough, it may be considered available. Therefore, in anexemplary embodiment, a threshold may be set. In this way, a decreasedpenalty value may be compared with the threshold to determine that thedecreased penalty value is small enough to cause a synchronizationsource to be considered available. Similar to the first period, secondperiod, penalty value, and count, the threshold also may be configurableor adjustable.

Therefore, in an exemplary embodiment, method 300 may comprise comparingdecreased penalty value with a threshold. If the decreased penalty valueis larger than or equal to the threshold, which means that penalty valueis not small enough and thus the synchronization source is stillinstable, the synchronization source thus may be identified as instable.In the case, method 300 may comprise restarting the second period tomonitor the synchronization source within second period as describedabove. If the decreased penalty value is less than the threshold, whichmeans that the penalty value is already small enough and thus thesynchronization source is stable, the synchronization source may beidentified as stable.

After a stability of a synchronization source is detected andidentified, the availability of the synchronization source may bedetermined accordingly. Therefore, in an exemplary embodiment, in method300, determining the availability of the synchronization source based onthe detected stability of the synchronization source may furthercomprise determining the synchronization source as available if thesynchronization source is identified as stable; or determining thesynchronization source as unavailable if the synchronization source isidentified as instable.

In most cases, there are typically many synchronization sources.However, if all of synchronization sources fail and thus are identifiedas instable, components or devices cannot select any synchronizationsource as a reference, it is undesired. In this case, thus, in someembodiments of method 300, determining the availability of asynchronization source based on the detected stability of thesynchronization source may further comprise determining thesynchronization source as available even if the synchronization sourceis identified as instable in the case that the synchronization source isused originally and/or the penalty value of the synchronization sourceis the smallest among all synchronization sources if all synchronizationsources are identified as instable. That is, even if all ofsynchronization sources fail and thus instable, one synchronizationsource should be selected as a reference. In this case, asynchronization source that is used originally may be consideredavailable or a synchronization source whose penalty value is thesmallest among all synchronization sources may be considered available.In this way, one synchronization source may be always selected as areference in any case for components or devices.

However, since the synchronization source that is selected as areference in the above case is actually unqualified, it is necessarythat this is prompted, e.g. notifying an operator of this. Therefore, insome embodiments, method 300 may further comprise generating an alarm ifthe synchronization source is determined as available when it isactually unqualified. To this end, method 300 can be performedindependently for each synchronization source.

It will be appreciated that method 300 described above with respect toFIG. 3 may be applied in any suitable devices or components in anysuitable communication system to achieve any synchronization, e.g.,frequency synchronization, phase/time synchronization, framesynchronization, etc. In other words, the method based on the principleof the present disclosure may be applied to any devices, components,systems, networks, and/or the combination thereof that may receivesynchronization sources and/or may provide synchronization sources,e.g., a router, a switch, etc.

Based on the above, it can be seen that the method of the presentdisclosure possesses many advantages over the manner of the WTR, e.g.,the method of the present disclosure may determine an availability of asynchronization source in a more flexible manner than the WTR.

FIG. 4 is a block diagram of a network device 400 for determining anavailability of a synchronization source in a communication systemaccording to an embodiment of the present disclosure. As shown in FIG.4, network device 400 may comprise a processor 410 and a memory 420. Thememory 420 may be communicatively coupled to the processor and adaptedto store instructions which, when executed by the processor 410, causenetwork device 400 to perform operations of detecting a stability of thesynchronization source when the synchronization source recovers from afailure; and determining the availability of a synchronization sourcebased on the detected stability of the synchronization source. Theinstructions stored in the memory 420 also may include those that, whenexecuted by the processor 410, cause network device 400 to implementother steps of the methods described with respect to FIG. 3 in additionthose steps described above with respect to FIG. 4. It will beappreciated that network device 400 may include any other suitablecomponents and may be implemented by any suitable technology.

The processor 410 may include one or more processing units. A processingunit may be a physical device or article of manufacture comprising oneor more integrated circuits that read data and instructions fromcomputer readable media, such as the memory 420, and selectively executethe instructions. In various embodiments, the processor 410 may beimplemented in various ways. As an example, the processor 410 may beimplemented as one or more processing cores. As another example, theprocessor 410 may comprise one or more separate microprocessors. In yetanother example, the processor 410 may comprise an application-specificintegrated circuit (ASIC) that provides specific functionality. In yetanother example, the processor 410 provides specific functionality byusing an ASIC and by executing computer-executable instructions.

The memory 420 may include one or more computer-usable orcomputer-readable storage medium capable of storing data and/orcomputer-executable instructions. It should be appreciated that thestorage medium is preferably a non-transitory storage medium.

It will be appreciated that network device 400 may comprise any othersuitable component.

FIG. 5 is a block diagram of another network device 500 for determiningan availability of a synchronization source in a communication systemaccording to an embodiment of the present disclosure. As shown in FIG.5, network device 500 may comprise a detecting component 510 and adetermining component 520. The detecting component 510 may be operableto detect a stability of the synchronization source when thesynchronization source recovers from a failure. The determiningcomponent 520 may be operable to determine the availability of asynchronization source based on the detected stability of thesynchronization source. It will be appreciated that network device 500also may include any other suitable component(s) that is/are operable toperform other steps of the method described with respect to FIG. 3 inaddition those steps described above with respect to FIG. 5.

In some embodiments, network device 500 also may include othercomponents that are operable to perform steps as described below. In anembodiment, the detecting the stability of the synchronization sourcewhen the synchronization source recovers from the failure may comprise:starting a first period when the synchronization source recovers fromthe failure; detecting within the first period whether there is the flapoccurred in the synchronization source; identifying the synchronizationsource as instable if the flap is detected in the synchronizationsource; or identifying the synchronization source as stable if no flapis detected in the synchronization source. In an embodiment, identifyingthe synchronization source as instable may further comprise setting apenalty value and a count for the flap detected in the synchronizationsource; increasing the penalty value and the count; starting a secondperiod; detecting within the second period whether there is anotherfailure in the synchronization source; restarting the first period whenthe synchronization source recovers from the another failure if theanother failure is detected in the synchronization source; or decreasethe penalty value if no another failure is detected in thesynchronization source; comparing decreased penalty value with athreshold; if the decreased penalty value is larger than or equal to thethreshold: identifying the synchronization source as instable;restarting the second period; or if the decreased penalty value is lessthan the threshold: identifying the synchronization source as stable. Inan embodiment, determining the availability of the synchronizationsource based on the detected stability of the synchronization source mayfurther comprise: determining the synchronization source as available ifthe synchronization source is identified as stable; or determining thesynchronization source as unavailable if the synchronization source isidentified as instable. In an embodiment, determining the availabilityof a synchronization source based on the detected stability of thesynchronization source may further comprise: determining thesynchronization source as available even if the synchronization sourceis identified as instable in the case that the synchronization source isused originally and/or the penalty value of the synchronization sourceis the smallest among all synchronization sources if all synchronizationsources are identified as instable. In an embodiment, an alarm may begenerated when the synchronization source is determined as available. Inan embodiment, the penalty value, the count, the threshold, the firstperiod, and the second period may be configurable. In an embodiment,initial values of the penalty value and the count may be configured tobe zero. In an embodiment, a maximum value of the penalty value may beconfigured such that the penalty value does not continue to increasewhen the penalty value reaches the maximum value. In an embodiment, thepenalty value may be based on the count. In an embodiment, decreasingthe penalty value may comprise decreasing penalty value faster thanincreasing the penalty value. In an embodiment, decreasing penalty valuefaster than increasing the penalty value may comprise decreasing thepenalty value exponentially.

FIG. 6 is a flowchart schematically illustrating a process 600 fordetermining an availability of a synchronization source in acommunication system according to an embodiment of the presentdisclosure. Process 600 is a process that can be applied to an existingcommunication system based on the principle of the present disclosure.In an existing communication system, there is typically a local logicthat is responsible for determining an availability of a synchronizationsource by using the WTR. The local logic may be used to implementprocess 600 based on the principle of the present disclosure. Toimplement process 600 in the local logic, some new events and new alarmsfor delivering message to the local logic or a human operator aredefined. However, it will be appreciated that process 600 may beimplemented in any other suitable logic, device, system, etc., in anyform of hardware, software, firmware, and any combination thereof.

As shown in FIG. 6, process 600 may start with a failure of asynchronization source. When the synchronization source fails, anindication of Signal Fail (SF) may be sent to the local logic to informthe local logic of the failure of the synchronization source. Theindication of SF also may trigger an alarm for notify a human operatorof failure of the synchronization source.

After the sending of an indication of SF, in process 600, it may bedecided whether the method of the present disclosure for determining anavailability of a synchronization source or the method using the WTR isenabled. If the method using the WTR is enabled, the logic may exit fromprocess 600 and may use the method of the WTR to determine anavailability of a synchronization (not shown). If the method of thepresent disclosure for determining the availability of thesynchronization source is enabled, process 600 will proceed to arecovery of the failing synchronization source.

In process 600, an observation period Tm may be started when thesynchronization source recovers from the failure to detect within theobservation period whether there is flap occurred in the synchronizationsource. The observation period is equivalent to the first perioddescribed above with respect to method 300 of FIG. 3.

The observation period may be configurable and may be implemented by atimer. It will be appreciated that the observation period may beimplemented by any suitable technology.

If there is no flap detected within the observation period or theobservation period is terminated as demand by an operator, process 600may exit, which means that the local logic considers the synchronizationsource stable and thus available. If flap is detected within theobservation period, an indication of Clear Signal Fail (Clear SF) may besent to the local logic to indicate the synchronization source hasrecovered. The indication of Clear SF also may clear the alarm triggeredby the indication of SF to notify a human operator of the recovery ofthe synchronization source.

After sending the indication of Clear SF, in process 600, a penaltyvalue and a count for the flap may be increased. That is, the stabilityof the synchronization source may be determined by means of the penaltyvalue and the number of the flap may be recorded.

The penalty value and the count may be configurable and initial valuesof the penalty value and the count may be configured to be zero. Thepenalty value and the count may be increased by equations below,respectively:the penalty value=min{2{circumflex over ( )}N*1000,X{1−(½){circumflexover ( )}[(t1−t0)/T]}+delta};  (1)the count=min{n+1,N};  (2)wherein X indicates the magnitude of penalty value over time;

N is defined as the maximum value of the count, which is used to avoid asynchronization source stays in Source Penalty (SP) state, as describedbelow, for an unpredictable long time; the max penalty value can bedefined accordingly based on N, for example, 1000*2{circumflex over( )}N;

t1 is current system time;

t0 is the system time when a decay time t as described below is started;and

the delta may be set and may be equal to 1000*2{circumflex over( )}(n−1) considering the existing system.

After increasing the penalty value and the count or at the same time, anevent (Source Penalty) defined newly occurs and an indication of SourcePenalty (SP) may be sent to the logic to indicate that although thesynchronization source has recovered from a failure but thesynchronization source is still instable because flap is detected.

In this case, in process 600, the decay time t may be started, which isequivalent to starting the second period described above with respect tomethod 300 of FIG. 3, to detect within the decay time whether there isanother failure in the synchronization source. The purpose of settingthe decay time is that if the synchronization source does not fail againwithin the decay time, the penalty value that represents its stabilitywill be decayed so that the synchronization source might be a candidateagain when the penalty value is decayed to certain extent.

The decay time may be also configurable and may be implemented by atimer. It will be appreciated that the decay time may be implemented byany suitable technology. The decay time also can be terminated as demandby an operator. When the decay time is terminated by the operator, anevent (Clear SP) defined newly occurs and an indication of Clear SP maybe sent to the logic to indicate the synchronization source is stableand thus available (not shown), and then process 600 may exit. At thesame time, the indication of Clear SP may clear the alarm triggered bythe indication of SP to notify a human operator of an availablesynchronization source.

If another failure is detected within the decay time, in process 600,the steps described above may be repeated to handle the failure. Thatis, in process 600, an indication of SF may be sent to the logic againand an alarm may be triggered, a recovery of the failing synchronizationsource may be waited for, the observation time may be restarted again,and the subsequent steps as described above may be performed. If noanother failure is detected in the decay time, in process 600, thepenalty value may be decreased. In an embodiment, the penalty value maybe decreased, i.e. a decay of the penalty value, in a manner thatdecreasing is faster than increasing. In another embodiment, the penaltyvalue may be decreased in a manner that decreasing is much faster thanincreasing, e.g. exponentially by an equation (3) below:the penalty value=X[1−(½){circumflex over ( )}(t/T)];  (3)wherein T is half decay life that is used to indicate a speed ofexponentially decreasing, e.g. five minutes.

Then, in process 600, the decreased penalty value that is calculated by,for example, the above equation (3) may be compared with a thresholdthat is configurable.

If decreased penalty value is larger than or equal to the threshold, inprocess 600, the decay time may be restarted to detect whether there isanother failure in the synchronization source. If there is no anotherfailure in the synchronization source, the penalty value will bedecreased continuously. If there is another failure, process 600 mayproceed as described above.

If the decreased penalty value is less than the threshold, thesynchronization source may be considered stable and available, and inprocess 600, an indication of Clear SP may be sent to the logic toindicate the synchronization source is stable and thus available, andprocess 600 then may exit. At the same time, the indication of Clear SPmay clear the alarm triggered by the indication of SP to notify a humanoperator of the available synchronization source.

In addition, process 600 may further comprise additional steps (notshown) for handling the case that all of provided synchronizationsources are considered instable. In the case that all of providedsynchronization sources are considered instable and thus areunavailable, i.e., all synchronization sources are in SP state, theremay be three options to handle this case: (1) determining thesynchronization source that is used originally as available; (2)determining the synchronization source as available whose penalty valueis the smallest among all synchronization sources; and (3) switchinginto holdover.

It will be appreciated that the order described above in which process600 is performed is merely exemplary and those steps performed insuccession also may be performed simultaneously.

It can be seen that process 600 not only possesses advantages mentionedabove but also may be used in conjunction with an existing logic, whichwill minimize the cost of deploying the method of the presentdisclosure.

It will be appreciated that the method and process described above maybe implemented by a non-transitory computer readable medium having acomputer program stored thereon, by a hardware, software, firmware,and/or any combination of thereof.

The present disclosure may also provide a memory containing the computerprogram as mentioned above, which includes machine-readable media andmachine-readable transmission media. The machine-readable media may alsobe called computer-readable media, and may include machine-readablestorage media, for example, magnetic disks, magnetic tape, opticaldisks, phase change memory, or an electronic memory terminal device likea random access memory (RAM), read only memory (ROM), flash memorydevices, CD-ROM, DVD, Blue-ray disc and the like. The machine-readabletransmission media may also be called a carrier, and may include, forexample, electrical, optical, radio, acoustical or other form ofpropagated signals, such as carrier waves, infrared signals, and thelike.

The techniques described herein may be implemented by various means sothat an apparatus implementing one or more functions of a correspondingapparatus described with an embodiment includes not only prior artmeans, but also means for implementing the one or more functions of thecorresponding apparatus described with the embodiment and it may includeseparate means for each separate function, or means that may beconfigured to perform two or more functions. For example, thesetechniques may be implemented in hardware (one or more apparatuses),firmware (one or more apparatuses), software (one or more modules), orcombinations thereof. For a firmware or software, implementation may bemade through modules (e.g., procedures, functions, and so on) thatperform the functions described herein.

Example embodiments herein have been described above with reference toblock diagrams and flowchart illustrations of methods and apparatuses.It will be understood that each block of the block diagrams andflowchart illustrations, and combinations of blocks in the blockdiagrams and flowchart illustrations, respectively, can be implementedby various means including hardware, software, firmware, and acombination thereof. For example, in one embodiment, each block of theblock diagrams and flowchart illustrations, and combinations of blocksin the block diagrams and flowchart illustrations can be implemented bycomputer program instructions. These computer program instructions maybe loaded onto a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions which execute on the computer or otherprogrammable data processing apparatus create means for implementing thefunctions specified in the flowchart block or blocks.

Further, while operations are depicted in a particular order, thisshould not be understood as requiring that such operations be performedin the particular order shown or in sequential order, or that allillustrated operations be performed, to achieve desirable results. Incertain circumstances, multitasking and parallel processing may beadvantageous. Likewise, while several specific implementation detailsare contained in the above discussions, these should not be construed aslimitations on the scope of the subject matter described herein, butrather as descriptions of features that may be specific to particularembodiments. Certain features that are described in this specificationin the context of separate embodiments can also be implemented incombination in a single embodiment. Conversely, various features thatare described in the context of a single embodiment can also beimplemented in multiple embodiments separately or in any suitablesub-combination. Moreover, although features may be described above asacting in certain combinations and even initially claimed as such, oneor more features from a claimed combination can in some cases be excisedfrom the combination, and the claimed combination may be directed to asub-combination or variation of a sub-combination.

It will be obvious to a person skilled in the art that, as thetechnology advances, the inventive concept can be implemented in variousways. The above described embodiments are given for describing ratherthan limiting the disclosure, and it is to be understood thatmodifications and variations may be resorted to without departing fromthe spirit and scope of the disclosure as those skilled in the artreadily understand. Such modifications and variations are considered tobe within the scope of the disclosure and the appended claims. Theprotection scope of the disclosure is defined by the accompanyingclaims.

The invention claimed is:
 1. A method for determining an availability ofa synchronization source in a communication system, comprises: detectinga stability of the synchronization source when the synchronizationsource recovers from a failure; and determining the availability of asynchronization source based on the detected stability of thesynchronization source, wherein the detecting the stability of thesynchronization source when the synchronization source recovers from thefailure comprises: starting a first period when the synchronizationsource recovers from the failure; detecting within the first periodwhether there is a flap occurred in the synchronization source; when theflap is detected in the synchronization source, identifying thesynchronization source as instable; when no flap is detected in thesynchronization source, identifying the synchronization source asstable; and wherein identifying the synchronization source as instablefurther comprises: setting a penalty value and a count for the flapdetected in the synchronization source; increasing the penalty value andthe count; starting a second period; detecting within the second periodwhether there is another failure in the synchronization source;restarting the first period when the synchronization source recoversfrom the another failure if the another failure is detected in thesynchronization source; or decreasing the penalty value if no anotherfailure is detected in the synchronization source; comparing decreasedpenalty value with a threshold; if the decreased penalty value is largerthan or equal to the threshold then identifying the synchronizationsource as instable and restarting the second period; or if the decreasedpenalty value is less than the threshold then identifying thesynchronization source as stable.
 2. The method of claim 1, whereindetermining the availability of the synchronization source based on thedetected stability of the synchronization source further comprises:determining the synchronization source as available if thesynchronization source is identified as stable; or determining thesynchronization source as unavailable if the synchronization source isidentified as instable.
 3. The method of claim 1, wherein determiningthe availability of a synchronization source based on the detectedstability of the synchronization source further comprises: determiningthe synchronization source as available even if the synchronizationsource is identified as instable in the case that the synchronizationsource is used originally or the penalty value of the synchronizationsource is the smallest among all synchronization sources if allsynchronization sources are identified as instable.
 4. The method ofclaim 3, further comprises generating an alarm when the synchronizationsource is determined as available when it is actually unqualified. 5.The method of claim 1, wherein the penalty value, the count, thethreshold, the first period, and the second period are configurable. 6.The method of claim 5, wherein initial values of the penalty value andthe count are configured to be zero.
 7. The method of claim 5, furthercomprises configuring a maximum value of the penalty value such that thepenalty value does not continue to increase when the penalty valuereaches the maximum value.
 8. The method of claim 1, wherein the penaltyvalue is based on the count.
 9. The method of claim 1, whereindecreasing the penalty value comprises decreasing penalty value fasterthan increasing the penalty value.
 10. The method of claim 9, whereindecreasing penalty value faster than increasing the penalty valuecomprises decreasing the penalty value exponentially.
 11. A networkdevice for determining an availability of a synchronization source in acommunication system, comprises: a processor; and a memorycommunicatively coupled to the processor and adapted to storeinstructions which, when executed by the processor, cause the networkdevice to perform operations of: detecting a stability of thesynchronization source when the synchronization source recovers from afailure; and determining the availability of a synchronization sourcebased on the detected stability of the synchronization source, whereinthe operation of detecting the stability of the synchronization sourcewhen the synchronization source recovers from a failure comprisesoperations of: starting a first period when the synchronization sourcerecovers from the failure; detecting within the first period whetherthere is a flap occurred in the synchronization source; when the flap isdetected in the synchronization source, identifying the synchronizationsource as instable; when no flap is detected in the synchronizationsource, identifying the synchronization source as stable; and whereinthe operation of identifying the synchronization source as instablefurther comprises operations of: setting a penalty value and a count forthe flap detected in the synchronization source; increasing the penaltyvalue and the count; starting a second period; detecting within thesecond period whether there is another failure in the synchronizationsource; restarting the first period when the synchronization sourcerecovers from the another failure if the another failure is detected inthe synchronization source; or decreasing the penalty value if noanother failure is detected in the synchronization source; comparingdecreased penalty value with a threshold; if the decreased penalty valueis larger than or equal to the threshold then identifying thesynchronization source as instable and restarting the second period; orif the decreased penalty value is less than the threshold thenidentifying the synchronization source as stable.
 12. The network deviceof claim 11, wherein the operation of determining the availability ofthe synchronization source based on the detected stability of thesynchronization source further comprises operations of: determining thesynchronization source as available if the synchronization source isidentified as stable; or determining the synchronization source asunavailable if the synchronization source is identified as instable. 13.The network device of claim 11, wherein the operation of determining theavailability of a synchronization source based on the detected stabilityof the synchronization source further comprises operations of:determining the synchronization source as available even if thesynchronization source is identified as instable in the case that thesynchronization source is used originally or the penalty value of thesynchronization source is the smallest among all synchronization sourcesif all synchronization sources are identified as instable.
 14. Thenetwork device of claim 13, further comprises an operation of generatingan alarm when the synchronization source is determined as available whenit is actually unqualified.
 15. The network device of claim 11, whereinthe penalty value, the count, the threshold, the first period, and thesecond period are configurable.
 16. The network device of claim 15,further comprises an operation of configuring a maximum value of thepenalty value such that the penalty value does not continue to increasewhen the penalty value reaches the maximum value.